diff --git a/llvm/include/llvm/Transforms/IPO/Attributor.h b/llvm/include/llvm/Transforms/IPO/Attributor.h
--- a/llvm/include/llvm/Transforms/IPO/Attributor.h
+++ b/llvm/include/llvm/Transforms/IPO/Attributor.h
@@ -289,6 +289,19 @@
   }
   ///}
 
+  /// Return true if the position refers to a function interface, that is the
+  /// function scope, the function return, or an argumnt.
+  bool isFnInterfaceKind() const {
+    switch (getPositionKind()) {
+    case IRPosition::IRP_FUNCTION:
+    case IRPosition::IRP_RETURNED:
+    case IRPosition::IRP_ARGUMENT:
+      return true;
+    default:
+      return false;
+    }
+  }
+
   /// Return the Function surrounding the anchor value.
   ///
   ///{
@@ -1035,6 +1048,27 @@
   IRAttribute(const IRPosition &IRP) : IRPosition(IRP) {}
   ~IRAttribute() {}
 
+  /// See AbstractAttribute::initialize(...).
+  virtual void initialize(Attributor &A) override {
+    if (hasAttr(getAttrKind())) {
+      this->getState().indicateOptimisticFixpoint();
+      return;
+    }
+
+    const IRPosition &IRP = this->getIRPosition();
+    bool IsFnInterface = IRP.isFnInterfaceKind();
+    const Function *FnScope = IRP.getAnchorScope();
+    // TODO: Not all attributes require an exact definition. Find a way to
+    //       enable deduction for some but not all attributes in case the
+    //       definition might be changed at runtime, see also
+    //       http://lists.llvm.org/pipermail/llvm-dev/2018-February/121275.html.
+    // TODO: We could always determine abstract attributes and if sufficient
+    //       information was found we could duplicate the functions that do not
+    //       have an exact definition.
+    if (IsFnInterface && (!FnScope || !FnScope->hasExactDefinition()))
+      this->getState().indicatePessimisticFixpoint();
+  }
+
   /// See AbstractAttribute::manifest(...).
   ChangeStatus manifest(Attributor &A) override {
     SmallVector<Attribute, 4> DeducedAttrs;
diff --git a/llvm/lib/Transforms/IPO/Attributor.cpp b/llvm/lib/Transforms/IPO/Attributor.cpp
--- a/llvm/lib/Transforms/IPO/Attributor.cpp
+++ b/llvm/lib/Transforms/IPO/Attributor.cpp
@@ -641,12 +641,6 @@
 struct AANoUnwindImpl : AANoUnwind {
   AANoUnwindImpl(const IRPosition &IRP) : AANoUnwind(IRP) {}
 
-  /// See AbstractAttribute::initialize(...).
-  void initialize(Attributor &A) override {
-    if (hasAttr({Attribute::NoUnwind}))
-      indicateOptimisticFixpoint();
-  }
-
   const std::string getAsStr() const override {
     return getAssumed() ? "nounwind" : "may-unwind";
   }
@@ -692,7 +686,7 @@
   void initialize(Attributor &A) override {
     AANoUnwindImpl::initialize(A);
     Function *F = getAssociatedFunction();
-    if (!F || !F->hasExactDefinition())
+    if (!F)
       indicatePessimisticFixpoint();
   }
 
@@ -752,7 +746,7 @@
     ReturnedValues.clear();
 
     Function *F = getAssociatedFunction();
-    if (!F || !F->hasExactDefinition()) {
+    if (!F) {
       indicatePessimisticFixpoint();
       return;
     }
@@ -771,6 +765,9 @@
         return;
       }
     }
+
+    if (!F->hasExactDefinition())
+      indicatePessimisticFixpoint();
   }
 
   /// See AbstractAttribute::manifest(...).
@@ -1137,12 +1134,6 @@
 struct AANoSyncImpl : AANoSync {
   AANoSyncImpl(const IRPosition &IRP) : AANoSync(IRP) {}
 
-  /// See AbstractAttribute::initialize(...).
-  void initialize(Attributor &A) override {
-    if (hasAttr({Attribute::NoSync}))
-      indicateOptimisticFixpoint();
-  }
-
   const std::string getAsStr() const override {
     return getAssumed() ? "nosync" : "may-sync";
   }
@@ -1310,7 +1301,7 @@
   void initialize(Attributor &A) override {
     AANoSyncImpl::initialize(A);
     Function *F = getAssociatedFunction();
-    if (!F || !F->hasExactDefinition())
+    if (!F)
       indicatePessimisticFixpoint();
   }
 
@@ -1336,12 +1327,6 @@
 struct AANoFreeImpl : public AANoFree {
   AANoFreeImpl(const IRPosition &IRP) : AANoFree(IRP) {}
 
-  /// See AbstractAttribute::initialize(...).
-  void initialize(Attributor &A) override {
-    if (hasAttr({Attribute::NoFree}))
-      indicateOptimisticFixpoint();
-  }
-
   /// See AbstractAttribute::updateImpl(...).
   ChangeStatus updateImpl(Attributor &A) override {
     auto CheckForNoFree = [&](Instruction &I) {
@@ -1380,7 +1365,7 @@
   void initialize(Attributor &A) override {
     AANoFreeImpl::initialize(A);
     Function *F = getAssociatedFunction();
-    if (!F || !F->hasExactDefinition())
+    if (!F)
       indicatePessimisticFixpoint();
   }
 
@@ -1409,6 +1394,8 @@
   void initialize(Attributor &A) override {
     if (hasAttr({Attribute::NonNull, Attribute::Dereferenceable}))
       indicateOptimisticFixpoint();
+    else
+      AANonNull::initialize(A);
   }
 
   /// See AbstractAttribute::getAsStr().
@@ -1514,14 +1501,6 @@
 struct AANoRecurseImpl : public AANoRecurse {
   AANoRecurseImpl(const IRPosition &IRP) : AANoRecurse(IRP) {}
 
-  /// See AbstractAttribute::initialize(...).
-  void initialize(Attributor &A) override {
-    if (hasAttr({getAttrKind()})) {
-      indicateOptimisticFixpoint();
-      return;
-    }
-  }
-
   /// See AbstractAttribute::getAsStr()
   const std::string getAsStr() const override {
     return getAssumed() ? "norecurse" : "may-recurse";
@@ -1548,7 +1527,7 @@
   void initialize(Attributor &A) override {
     AANoRecurseImpl::initialize(A);
     Function *F = getAssociatedFunction();
-    if (!F || !F->hasExactDefinition())
+    if (!F)
       indicatePessimisticFixpoint();
   }
 
@@ -1601,10 +1580,7 @@
 
   /// See AbstractAttribute::initialize(...).
   void initialize(Attributor &A) override {
-    if (hasAttr({Attribute::WillReturn})) {
-      indicateOptimisticFixpoint();
-      return;
-    }
+    AAWillReturn::initialize(A);
 
     Function *F = getAssociatedFunction();
     if (containsPossiblyEndlessLoop(F))
@@ -1651,7 +1627,7 @@
   void initialize(Attributor &A) override {
     AAWillReturnImpl::initialize(A);
     Function *F = getAssociatedFunction();
-    if (!F || !F->hasExactDefinition())
+    if (!F)
       indicatePessimisticFixpoint();
   }
 
@@ -1678,12 +1654,6 @@
 struct AANoAliasImpl : AANoAlias {
   AANoAliasImpl(const IRPosition &IRP) : AANoAlias(IRP) {}
 
-  /// See AbstractAttribute::initialize(...).
-  void initialize(Attributor &A) override {
-    if (hasAttr({Attribute::NoAlias}))
-      indicateOptimisticFixpoint();
-  }
-
   const std::string getAsStr() const override {
     return getAssumed() ? "noalias" : "may-alias";
   }
@@ -1785,7 +1755,7 @@
   void initialize(Attributor &A) override {
     AANoAliasImpl::initialize(A);
     Function *F = getAssociatedFunction();
-    if (!F || !F->hasExactDefinition())
+    if (!F)
       indicatePessimisticFixpoint();
   }
 
@@ -2179,6 +2149,12 @@
       takeKnownDerefBytesMaximum(Attr.getValueAsInt());
 
     NonNullAA = &A.getAAFor<AANonNull>(*this, getIRPosition());
+
+    const IRPosition &IRP = this->getIRPosition();
+    bool IsFnInterface = IRP.isFnInterfaceKind();
+    const Function *FnScope = IRP.getAnchorScope();
+    if (IsFnInterface && (!FnScope || !FnScope->hasExactDefinition()))
+      indicatePessimisticFixpoint();
   }
 
   /// See AbstractAttribute::getState()
@@ -2333,7 +2309,7 @@
   void initialize(Attributor &A) override {
     AADereferenceableImpl::initialize(A);
     Function *F = getAssociatedFunction();
-    if (!F || !F->hasExactDefinition())
+    if (!F)
       indicatePessimisticFixpoint();
   }
 
@@ -2501,7 +2477,7 @@
   void initialize(Attributor &A) override {
     AAAlignImpl::initialize(A);
     Function *F = getAssociatedFunction();
-    if (!F || !F->hasExactDefinition())
+    if (!F)
       indicatePessimisticFixpoint();
   }
 
@@ -2531,12 +2507,6 @@
     return getAssumed() ? "noreturn" : "may-return";
   }
 
-  /// See AbstractAttribute::initialize(...).
-  void initialize(Attributor &A) override {
-    if (hasAttr({getAttrKind()}))
-      indicateOptimisticFixpoint();
-  }
-
   /// See AbstractAttribute::updateImpl(Attributor &A).
   virtual ChangeStatus updateImpl(Attributor &A) override {
     auto CheckForNoReturn = [](Instruction &) { return false; };
@@ -2562,7 +2532,7 @@
   void initialize(Attributor &A) override {
     AANoReturnImpl::initialize(A);
     Function *F = getAssociatedFunction();
-    if (!F || !F->hasExactDefinition())
+    if (!F)
       indicatePessimisticFixpoint();
   }
 
@@ -2592,10 +2562,7 @@
 
   /// See AbstractAttribute::initialize(...).
   void initialize(Attributor &A) override {
-    if (hasAttr(Attribute::NoCapture)) {
-      indicateOptimisticFixpoint();
-      return;
-    }
+    AANoCapture::initialize(A);
 
     const IRPosition &IRP = getIRPosition();
     const Function *F =
@@ -2604,8 +2571,7 @@
     // Check what state the associated function can actually capture.
     if (F)
       determineFunctionCaptureCapabilities(*F, *this);
-
-    if (!F || !F->hasExactDefinition())
+    else
       indicatePessimisticFixpoint();
   }
 
@@ -2992,7 +2958,7 @@
     }
 
     CallSite CS(U.getUser());
-    if (!CS || !CS.isCallee(&U) || !CS.getCaller()->hasExactDefinition()) {
+    if (!CS || !CS.isCallee(&U)) {
       if (!RequireAllCallSites)
         continue;
 
@@ -3022,7 +2988,7 @@
   // Since we need to provide return instructions we have to have an exact
   // definition.
   const Function *AssociatedFunction = IRP.getAssociatedFunction();
-  if (!AssociatedFunction || !AssociatedFunction->hasExactDefinition())
+  if (!AssociatedFunction)
     return false;
 
   // If this is a call site query we use the call site specific return values
@@ -3042,7 +3008,7 @@
 
   const IRPosition &IRP = QueryingAA.getIRPosition();
   const Function *AssociatedFunction = IRP.getAssociatedFunction();
-  if (!AssociatedFunction || !AssociatedFunction->hasExactDefinition())
+  if (!AssociatedFunction)
     return false;
 
   // TODO: use the function scope once we have call site AAReturnedValues.
@@ -3064,7 +3030,7 @@
   const IRPosition &IRP = QueryingAA.getIRPosition();
   // Since we need to provide instructions we have to have an exact definition.
   const Function *AssociatedFunction = IRP.getAssociatedFunction();
-  if (!AssociatedFunction || !AssociatedFunction->hasExactDefinition())
+  if (!AssociatedFunction)
     return false;
 
   // TODO: use the function scope once we have call site AAReturnedValues.
@@ -3569,25 +3535,16 @@
   Attributor A(InfoCache, DepRecInterval);
 
   for (Function &F : M) {
-    // TODO: Not all attributes require an exact definition. Find a way to
-    //       enable deduction for some but not all attributes in case the
-    //       definition might be changed at runtime, see also
-    //       http://lists.llvm.org/pipermail/llvm-dev/2018-February/121275.html.
-    // TODO: We could always determine abstract attributes and if sufficient
-    //       information was found we could duplicate the functions that do not
-    //       have an exact definition.
-    if (!F.hasExactDefinition()) {
+    if (F.hasExactDefinition())
+      NumFnWithExactDefinition++;
+    else
       NumFnWithoutExactDefinition++;
-      continue;
-    }
 
     // For now we ignore naked and optnone functions.
     if (F.hasFnAttribute(Attribute::Naked) ||
         F.hasFnAttribute(Attribute::OptimizeNone))
       continue;
 
-    NumFnWithExactDefinition++;
-
     // Populate the Attributor with abstract attribute opportunities in the
     // function and the information cache with IR information.
     A.identifyDefaultAbstractAttributes(F);
diff --git a/llvm/test/Transforms/FunctionAttrs/arg_returned.ll b/llvm/test/Transforms/FunctionAttrs/arg_returned.ll
--- a/llvm/test/Transforms/FunctionAttrs/arg_returned.ll
+++ b/llvm/test/Transforms/FunctionAttrs/arg_returned.ll
@@ -796,6 +796,33 @@
   ret i32 %PHI2
 }
 
+define weak_odr i32 @non_exact_0() {
+  ret i32 0
+}
+define weak_odr i32 @non_exact_1(i32 %a) {
+  ret i32 %a
+}
+define weak_odr i32 @non_exact_2(i32 returned %a) {
+  ret i32 %a
+}
+define weak_odr i32* @non_exact_3(i32* align 32 returned %a) {
+  ret i32* %a
+}
+define i32 @exact(i32* %a) {
+  %c0 = call i32 @non_exact_0()
+  %c1 = call i32 @non_exact_1(i32 1)
+  %c2 = call i32 @non_exact_2(i32 2)
+  %c3 = call i32* @non_exact_3(i32* %a)
+  %c4 = load i32, i32* %c3
+; FIXME: %c2 should be replaced but not %c0 or %c1!
+; CHECK:  %add1 = add i32 %c0, %c1
+; CHECK:  %add2 = add i32 %add1, %c2
+; CHECK:  %add3 = add i32 %add2, %c3
+  %add1 = add i32 %c0, %c1
+  %add2 = add i32 %add1, %c2
+  %add3 = add i32 %add2, %c4
+  ret i32 %add3
+}
 
 attributes #0 = { noinline nounwind uwtable }
 
diff --git a/llvm/test/Transforms/FunctionAttrs/nonnull.ll b/llvm/test/Transforms/FunctionAttrs/nonnull.ll
--- a/llvm/test/Transforms/FunctionAttrs/nonnull.ll
+++ b/llvm/test/Transforms/FunctionAttrs/nonnull.ll
@@ -458,4 +458,14 @@
   ret i32* %c
 }
 
+; ATTRIBUTOR: define internal void @called_by_weak(i32* nocapture nonnull %a)
+define internal void @called_by_weak(i32* %a) {
+  ret void
+}
+
+define weak_odr void @weak_caller(i32* nonnull %a) {
+  call void @called_by_weak(i32* %a)
+  ret void
+}
+
 attributes #0 = { "null-pointer-is-valid"="true" }
diff --git a/llvm/test/Transforms/FunctionAttrs/noreturn_async.ll b/llvm/test/Transforms/FunctionAttrs/noreturn_async.ll
--- a/llvm/test/Transforms/FunctionAttrs/noreturn_async.ll
+++ b/llvm/test/Transforms/FunctionAttrs/noreturn_async.ll
@@ -1,4 +1,4 @@
-; RUN: opt -functionattrs -attributor -attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=3 -S < %s | FileCheck %s
+; RUN: opt -functionattrs -attributor -attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=4 -S < %s | FileCheck %s
 ;
 ; This file is the same as noreturn_sync.ll but with a personality which
 ; indicates that the exception handler *can* catch asynchronous exceptions. As
diff --git a/llvm/test/Transforms/FunctionAttrs/nounwind.ll b/llvm/test/Transforms/FunctionAttrs/nounwind.ll
--- a/llvm/test/Transforms/FunctionAttrs/nounwind.ll
+++ b/llvm/test/Transforms/FunctionAttrs/nounwind.ll
@@ -1,5 +1,5 @@
 ; RUN: opt < %s -functionattrs -S | FileCheck %s
-; RUN: opt < %s -attributor -attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=4 -S | FileCheck %s --check-prefix=ATTRIBUTOR
+; RUN: opt < %s -attributor -attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=6 -S | FileCheck %s --check-prefix=ATTRIBUTOR
 
 ; TEST 1
 ; CHECK: Function Attrs: norecurse nounwind readnone